FIG. 1 shows a conventional clamping apparatus for cutting insert, which employs an L-shaped clamp lever (7) and a fixing screw (5) for pressing the lever to fix a cutting insert (1) having a through-hole onto a pocket (9) of a tool holder (3).
FIGS. 2 and 3 show a clamping apparatus for a cutting insert disclosed in Japanese Patent No. 2,877,140. The L-shaped clamp lever (7) is placed in a mounting bore (10) of the tool holder (3). The cutting insert (1) is then mounted on a pocket (9) of the tool holder (3). A clamp portion (7a) of the clamp lever (7) is inserted through a through-hole (1a) of the cutting insert (1). A screw hole (8) is formed from the side surface of the tool holder (3) to the mounting bore (10). The fixing screw (5) is fastened through the screw hole (8) until an inclined surface (5a) of a conically-shaped end of the fixing screw (5) contacts a lever portion (7b) of the clamp lever (7). The fixing screw (5) exerts pressure on the clamp lever (7) as the inclined surface (5a) slides along the top surface of the lever portion (7b). The clamp (7) rotates clockwise about a support portion (7c). Further, the clamp portion (7a) presses the cutting insert (1) downward against the pocket (9) of the tool holder (3) as it contacts the inside wall of a through-hole (1a) of the cutting insert (1). This fixes the cutting insert (1) on the pocket (9) of the tool holder (3).
The clamping force, by which the clamp portion (7a) of the clamp lever (7) presses down the cutting insert (1) through the through-hole (1a), is generated when the fixing screw (5) presses down the lever portion (7b) of the clamp lever (7). Preferably, the fixing screw (5) would be inserted vertically to directly press down the lever portion (7b) of the clamp lever (7). However, in a machining tool such as a Swiss-style lathe that uses multiple tool holders together, the gap between the tool holders is small. As such, the fixing screw (5) should be inserted through the side of the tool holder due to space constraints.
However, similar to the clamp lever (7) disclosed in Japanese Patent No. 2,877,140, when an inclined surface of a conically-shaped end of the fixing screw (5) exerts pressure on the clamp lever (7) by sliding against the lever portion (7b) of the clamp lever (7), a considerable amount of the applied pressure of the fixing screw (5) is distributed to press the lever portion (7b) against the support portion (7c), which does not contribute to the clamping action of the cutting insert. As a result, the pressure by the fixing screw (5) is less distributed for pressing down the lever portion (7b), which contributes to the clamping action of the cutting insert, thereby preventing the cutting insert from being firmly clamped on the tool holder.
Further, a preferable surface-to-surface contact between the lever portion (7b) and the fixing screw (5) cannot be made in the conventional L-shaped clamp lever (7) since the lever portion (7b) and the fixing screw (5) make a line contact, or since the contact is made as the two curved surfaces move relative to each other. If a strong load is applied to the cutting insert (1), then sliding between the fixing screw (5) and the lever portion (7b) occurs at the contacted portion. Such sliding causes a displacement of the fixing screw (5) and the lever portion (7b) to prevent a stable clamping.
Moreover, sliding of the fixing screw (5) on the lever portion (7b) by rotating the fixing screw tends to wear out the contacted portion. If such sliding is repeated several times, then the contacted portion becomes severely worn out, which displaces the contacted portion between the fixing screw (5) and the lever portion (7b). The resulting displacement of the fixing screw (5) and the lever portion (7b) relative to each other in the clamping state leads to an unstable clamping state.